1. Field of the Invention
The present invention relates to the use of diamond for various applications, such as chemical vapor-deposited (CVD) synthetic diamond coatings applied to a variety of light-transmissive substrates or free-standing bulk diamond. Diamond possesses unique superior properties including hardness, chemical inertness, and optical transparency from the ultra-violet to the far-infrared, which make it an ideal optical material for use as a protective optical coating material, an IR window, a missile or spacecraft dome or window and/or other utility in which severe environmental conditions of high-speed rain erosion and particle impact, aerodynamic heating and chemical attack problems may be encountered.
While diamond possesses the aforementioned superior properties which are highly desirable, it also has a high refraction index of about 2.4, which causes diamonds to reflect back about 30% of the incident light which strikes the surfaces thereof. While this property causes diamonds to sparkle or flash back reflected light to a high degree and to be extremely valuable as gems, it detracts seriously from the use of diamond as a protective optical material in which high optical transmission properties are desirable.
2. Discussion of the Prior Art
It is known that the reflective losses of optically transparent materials can be reduced by applying to the surface thereof antireflection coatings. While such coatings could be applied to a diamond surface, to reduce or eliminate light reflection, this would also nullify some of the necessary properties which justify the expense of using diamond, namely the surface hardness, temperature resistance, etc., responsible for the protective properties afforded by diamond. Moreover, there is a problem of providing a sufficient bond between diamond and an antireflective coating to withstand extreme environmental conditions. Other light-transmissive materials having lower refraction indexes are used as optical windows, such as quartz, glass, sapphire, etc., but the protective properties of such materials are far inferior to those of diamond, and they are not transparent in the mid- and far-infrared regions.
It is known that the optical properties of amorphous materials, such as silica glass, can be modified by ion implantation to increase the index of refraction of the glass and thus produce optical waveguides having controlled, reproducible light reflective properties. It is also known that such ion implantation is not effective for this purpose on certain materials, such as crystalline quartz and certain lithium ferroelectrics, since ion implantation was found to reduce the index of refraction thereof rather than increase the index as desired. Reference is made to the Treatise On Materials Science And Technology, published by Academic Press, Inc. (1980), Volume 18, pages 1 to 7 and 445-459.